1. Field of the Invention
The present invention generally relates to an antifriction bearing in which a rotating member of the bearing supports an encoder and a nonrotating member of the bearing supports a sensor that may be used to determine rotation parameters such as the speed or the angular position of the rotating element supporting the encoder. The present invention also relates to antifriction bearings for use in electric motors, which are required to operate in severe speed and temperature conditions.
2. Description of the Relevant Art
French Patent No. 2,754,903, describes an antifriction bearing that includes a sensor on the nonrotating track, of the Hall effect probe type, and an encoder on the rotating track moving in rotation with a slight air gap relative to the sensor while being capable of producing in the sensor a periodic signal with a frequency proportional to the rotation speed of rotation of the rotating track. The encoder includes an annular active portion. The annular active portion includes a plastic magnet and an active portion placed opposite the sensor. The active portion may be supplemented by a reinforcement portion that includes two annular elements placed in contact with the active portion on either side of the active zone.
This type of antifriction bearing is usually satisfactory, particularly in the field of electric motors. However, this type of encoder cannot operate at temperatures above 120°. In addition, the sensor and the encoder do not operate satisfactorily if they are subjected to high intensity external magnetic fields, for example the magnetic fields induced by the coils of the stator of electric motors and/or by the electromagnetic brake built into the motors. Finally, the axial compactness of this type of antifriction bearing is not optimal and is not easy to incorporate.
In high power asynchronous electric motors, control of the motor requires detection of the rotation parameters of the motor. Knowledge of speed and direction of rotation of the rotor may be needed to adapt the frequency and the direction of the current entering the coils of the stator. The use of a multipolar type encoder associated with a Hall effect probe is suitable only for applications in which the power and the control requirements are relatively imprecise, for example for a fan motor that operates at constant speed during use. Optical type sensor encoder systems, such as industrial encoders, require a mechanical interface for driving by the electric motor and are relatively sensitive to impacts and to temperature. Optical type sensor encoder systems are not likely to be built into a motor.
The invention aims to remedy these disadvantages.